Recently, with the breakthrough advancement of the manufacturing technique of light-emitting diodes (LEDs), the luminance and efficiency of the light-emitting diodes are greatly improved. The LED has replaced old fluorescent lamps as the illuminating device of the next generation. Nowadays, the LED has been widely employed in the applications of home illuminating appliances, car illuminating devices, handheld illuminating devices, the backlight source of LCD panels, traffic signal indicators, and billboards. In order to increase the luminance of the LED, a number of LEDs are connected in series to form a LED assembly.
LEDs are generally DC loads. In the application where a number of parallel-connected LED assemblies are employed, the current flowing through the LED assemblies are different from each other as the characteristics and impedance of each LED are different from each other. If the currents flowing through the LED assemblies are not balanced, the luminance will not be uniform and the longevity of respective LED will be shortened. This would further impair the electronic device.
In order to tackle the problem that the currents of the LED assemblies are not uniform, several current balancing techniques have been proposed to address this problem. One of such techniques is to employ independent drivers to individually drive each LED assembly. However, such independent driver will complicate the circuitry and increase the manufacturing cost. More disadvantageously, the current balancing effect is bad as the driver has tolerance. Another state-of-the-art current balancing technique is to use a common choke to equal the currents flowing through the LED assemblies. Nonetheless, using a plurality of common chokes will increase the number of magnetic elements in the circuitry, and thus the manufacturing cost is elevated and the size of the circuitry is expanded. More disadvantageously, the current balancing effect is also bad as the common choke will induce a magnetizing current.
Hence, it is needed to develop a current balancing circuit for addressing the aforementioned problems encountered by the prior art.